Optimal demodulation of signals in additive white Gaussian noise channels requires that the receive filter be matched to the transmit filter. A wireless communication device, however, generally uses analog filters in its receive portion for anti-aliasing and selectivity purposes. Unfortunately, the frequency and time domain responses of analog filters can vary over process, temperature, and supply voltage. Thus, in the prior art it has not been possible to maintain a fixed composite response in the receiver that is matched to the transmit filter in the base station throughout the operational life and environmental range of the wireless device without using a training sequence originating from the base transmitter. Such non-optimal, unmatched filtering can degrade the receiver sensitivity by more than 1 dB. Further, for high data rate systems such as those commonly referred to as 2.5G and 3G systems, a 1 dB sensitivity loss can lead to significant loss in system throughput and capacity.
Thus, what is needed is a method and apparatus for compensating for variations in the receive portion of a wireless communication device. Preferably, the method and apparatus will provide near-optimal matched filtering and, hence, greatly improved receiver performance over the operating life of the wireless communication device.